Electrostatically focused electron beam phase shifter



April 18, 1967 B. J. UDELSON ELECTROSTATICALLY FOCUSED ELECTRON BEAM PHASE SHIFTER Filed July 15, 1963 ZZUKW mvZChZIfi mmZTE AT do ddv fina Imsu INVENTOE,

fiuera/vd. Uaszso/v United States Patent 3,315 117 ELECTROSTATICALLY FQQUSED ELETRON BEAM PHASE SHIFTER Burton J. Udelscn, Bethesda, Md, assignor to the United States of America as represented by the Secretary of the Arm y Filed July 15, 1963, 5st. No. 295,255

4 Claims. (Cl. 315-3) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to phase shifters, and more particularly to an electronic phase shifter for operation at microwave frequencies.

The object of this invention is to provide a light weight, compact, high speed, high power, stable, linear, electrically controlled, microwave phase shifter. With the increased interest in electronically scanned antenna array systems, the importance of microwave electrically controlled phase shifters has been considerably increased. As presently contemplated, antenna arrays require a large number of phase shifters mounted in close proximity to each other. Ferrite phase shifters are now commonly used for this application. While these ferrite phase shifters have many of the desirable characteristics listed as objects of this invention, they tend to be limited, notably in their power handling capability, and also in the degree of linearity for large phase shifts.

Another object of this invention is to provide a voltage tunable microwave phase shifter which can be tuned either with a varying DC. voltage, or equally well with an applied A.C. or RF signal. The phase shifter of the instant invention permits, therefore, not only the standard low frequency phase shifting applications, such as antenna scanning, but also phase modulation.

A further object of the invention is the elimination of the magnetic field, or more specifically, the apparatus required to produce a magnetic field, commonly associated with voltage tunable microwave phase shifters.

These and other objects of this invention are achieved in applicants novel electron beam, electrostatically fo cused, phase shifter. This device includes an electron gun which produces a ribbon type beam of electrons, and a collector. Spaced intermediate between the electron gun and the collector is in succession, an input coupler, a drift space, and an output coupler. The input coupler couples the signal to be shifted in phase, or phase modulated, onto the electron beam. By varying the average DC. potential on the electrostatic focusing plates in this drift region, the phase of the RF signal on the electron beam may be varied linearly. The output coupler extracts the signal energy from the electron beam and applies it to a load circuit.

The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing.

The figure represents one specific embodiment of this invention.

Referring to the figure, there is shown a phase shifter embodying the principles of this invention. It includes an array of pairs of parallel planar plates 11 and 12, between which an electron sheet beam can pass. These plates are divided into three distinct regions, an input coupler 13, a phase shifting region 14, and an output coupler 15. Adjacent the input couple-r 13 is an electron gun 16, and adjacent the output coupler 15 is a collector 17. The RF signal which is to be shifted in phase, or phase modulated, is applied push-pull at input transformer 18, and is coupled onto the electron beam 10 in the form of a -fast wave at the input coupler 13. Similarly, the phase shifted signal appears at output transformer 19, having been coupled from the electron beam 10 by the fast wave output coupler 15.

Two D.C. supply voltages 21 and 22 are provided, and these voltages V and V are applied to alternate pairs of focusing plates 11 and 12, respectively, in all three sections of the phase shifter to provide electrostatic focusing of the electron sheet beam 10. The various regions of the tube having common D.C. potentials are isolated RF- wise from each other by appropriately placed chokes 23. The input coupler 13 and output coupler 14 are of the resonant fast wave type, and all the plates 11 and 12 on either side of the electron beam are maintained at the same RF potential by means of capacitors 24.

The electrostatic focusing mechanism and coupling mechanism used here are well known in the art, but a brief description will be included at this point for continuity. Electron focusing in the phase shifter of this invention is caused by transverse components of electric field established between individual pairs of plates 11 and 12. Along a center plane indicated by center line 25 the transverse electric field is zero; it increases with distance from the center line 25. Consequently, it may be shown that the electrons of the beam are subject to a force which tends to accelerate them away from a center plane 25 in regions of high potential and to accelerate them toward the center plane in low-potential regions, so that small ripples are imposed upon the electron trajectories. The low potential regions, however, exert the major influence because the electrons are farther from the center plane as they traverse these regions and are consequently in a stronger field; at the same time the electrons move more slowly through the low-potential regions and hence require more time to traverse them. The two effects are equally strong and result in a net force tending to deflect the electrons toward the center plane 25 of the reference path. This effect is comparable to an elastic force; consequently, the beam electrons follow simple harmonic motion trajectories centered about the center plane 25 of the reference path.

The lens voltages V and V required to obtain a given electron resonance frequency are substantially independent of the beam current, since the transverse resonant elastic field frequency is not dependent upon beam intensity, as is apparent from the approximate equation for determining this frequency,

where:

periodic potential component along the center plane.

A signal having a frequency substantially equal to the transverse-resonant frequency is applied to the deflectors 11 and 12 in the input coupler region 13. The applied signal establishes a transverse deflection field which produces excursions of the electron beam from the reference path center line 25 at the resonant frequency. As the beam traverses the output electrode system of output coupler 15, the transverse excursion of the electron beam 10 induces a signal in the output coupler 15.

When the natural resonant frequency of the electron beam 10 in the phase shifting region 14 is approximately equal to the beam resonant frequency in the couple-rs 13 and 15, the phase shift in the phase shifting section is given approximately by the equation:

@ liez where:

w=the input radian frequency from the coupler 13,

w =the natural resonant radian frequency of the electron beam in the phase shifting section,

v=the electron beam velocity in the phase shifting section,

Z=the length of the phase shifting section.

In the phase shifting region itself, the natural resonant radian frequency of the electron beam is determined by the voltages on the plates 11 and 12 in the phase shifting section. This frequency is given approximately by the equation:

K=a constant of proportionality depending upon the physical dimensions of the phase shifting section; princi pally, the longitudinal periodicity and lateral spacing between opposing plates 11 and 12,

V a and V =the instantaneous (D.C.+A.C.) voltages on the plates of the phase shifting section.

A phase shift of the signal on the output coupler with respect to that on the input coupler 13 is achieved simply by varying one or both of the voltages on the plates 11 and 12 in the phase shifting region thereby varying the transverse resonant frequency of the beam. Of course, by varying the frequency the wavelength is changed by a proportional amount causing the phase at the output of phase shifting region 14 to be changed with respect to the phase at the input of the region by a proportional amount. This may be accomplished by any of several methods. If linearity of phase shift with respect to an applied phase shifting signal is desired, a push-pull AC. or RF phase shifting signal is introduced at the terminals 26. With an RF signal the input signal will be phase modulated. Alternately, if the plates in the phase shifting region are disconnected from the common potentials 21 and 22 by means of switches 28 and 29, and are connected to two separate D.C. sources 31 and 32, then the amount of phase shift may be controlled 'by varying the sources 31 and 32.

The electrostatically focused phase shifter just described acts as an isolator between the input 18 and the output 19, providing resistive input and output terminations. Also, in addition to being simple, and light weight, since the electrostatically focused phase shifter of this invention employs a sheet electron beam, it is capable of transferring a large amount of RF power.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim as my invention:

1. A light weight, high power, phase shifter comprismg:

(a) an electron gun and a collector longitudinally dis placed therefrom,

(b) an electrostatically focused input coupler adjacent said electron gun and an electrostatically focused output coupler adjacent said collector with signal input means connected to said input coupler and signal output means connected to said output coupler,

(c) an electrostatically focused phase shift region between said input coupler and said output coupler, said electrostatically focused phase shifting region including a plurality of electrostatic focusing lenses, the strength of said lenses being such that an electron beam produced by said electron gun has a difierent natural resonant frequency in said input coupler and said phase shifting regions,

(d) means to vary the focusing lens strength in said phase shifting region thereby varying the transverse natural resonant frequency of said beam and varying the phase of said beam.

2. A light weight, high power, phase shifter compris- (a) an electron gun and a collector longitudinally displaced therefrom,

(b) an electrostatically focused input coupler adjacent said electron gun and an electrostatically focused output coupler adjacent said collector with signal input means connected to said input coupler and signal output means connected to said output coupler,

(c) an electrostatically focused phase shift region between said input coupler and said output coupler, said electrostatically focused phase shifting region including a plurality of electrostatic focusing lenses, the strength of said lenses being such that an electron beam produced by said electron gun has a different natural resonant frequency in said input coupler and said phase shifting regions, said focusing lenses including a plurality of pairs of opposed plates maintained at a predetermined DC. potential,

(d) and means to vary said average DC. potential on said plurality of plates thereby varying the transverse natural resonant frequency of said beam and varying the phase of said beam.

3. The method of shifting the phase of an electrical signal comprising the steps:

(a) applying a signal which is to be shifted in phase to an input coupler of an electron beam tube which has an electron gun, a collector longitudinally spaced therefrom, an electrostatically focused input coupler adjacent said electron gun, an electrostatically focused output coupler adjacent said collector, and an electrostatically focused phase shifting region having a plurality of focusing lenses intermediate said input and output coupler,

(b) applying an average DC potential to the focusing lenses in said electrostatically focused phase shifting region so that an electron beam produced by said electron gun has a natural resonant frequency which is different in said phase shifting region and said input coupler region,

(c) varying the strength of said focusing lenses thereby varying the transverse natural resonant frequency of said beam to vary the amount of phase shift in said applied signal.

4. The method of shifting the phase of an electrical signal comprising the steps:

(a) applying a signal which is to be shifted in phase to an input coupler of an electron beam tube which has an electron gun, a collector longitudinally spaced therefrom, an electrostatically focused input coupler adjacent said electron gun, an electrostatically focused output coupler adjacent said collector, and an electrostatically focused phase shifting region having a plurality of focusing lenses intermediate said input and output coupler,

(b) applying an average DC. potential to the focusing 3,3 1 5, 1 1 7 5 6 lenses in said eleetrostatically focused phase shifting References Cited by the Examiner region so that an electron beam produced by said UNITED STATES PATENTS electron gun has a natural resonant frequency which is different in said phase shifting region d Said 2,811,664 10/ 1957 Kazan 3l53.6 input coupler region, 5 3,050,657 96 Branch 315-3.6

(c? varying said average DC. potential thereby vary- HERMAN KARL SAALBACH, Primary Examiner.

ing the transverse natural resonant frequency of said beam to vary the amount of phase shift in said ap- ELI LIEBERMAN Examinerp i d g l- R. D. COHN, Assistant Examiner. 

1. A LIGHT WEIGHT, HIGH POWER, PHASE SHIFTER COMPRISING: (A) AN ELECTRON GUN AND A COLLECTOR LONGITUDINALLY DISPLACED THEREFROM, (B) AN ELECTROSTATICALLY FOCUSED INPUT COUPLER ADJACENT SAID ELECTRON GUN AND AN ELECTROSTATICALLY FOCUSED OUTPUT COUPLER ADJACENT SAID COLLECTOR WITH SIGNAL INPUT MEANS CONNECTED TO SAID INPUT COUPLER AND SIGNAL OUTPUT MEANS CONNECTED TO SAID OUTPUT COUPLER, (C) AN ELECTROSTATICALLY FOCUSED PHASE SHIFT REGION BETWEEN SAID INPUT COUPLER AND SAID OUTPUT COUPLER, SAID ELECTROSTATICALLY FOCUSED PHASE SHIFTING REGION INCLUDING A PLURALITY OF ELECTROSTATIC FOCUSING LENSES, THE STRENGTH OF SAID LENSES BEING SUCH THAT AN ELECTRON BEAM PRODUCED BY SAID ELECTRON GUN HAS A DIFFERENT NATURAL RESONANT FREQUENCY IN SAID INPUT COUPLER AND SAID PHASE SHIFTING REGIONS, (D) MEANS TO VARY THE FOCUSING LENS STRENGTH IN SAID PHASE SHIFTING REGION THEREBY VARYING THE TRANSVERSE NATURAL RESONANT FREQUENCY OF SAID BEAM AND VARYING THE PHASE OF SAID BEAM. 